This invention relates to a heat shield with thermal, acoustical and/or vibrational abatement properties and, in particular, to a heat shield for an exhaust system of an internal combustion engine.
Heat shields for exhaust systems of internal combustion engines are known, for example, as described in U.S. Pat. No. 5,590,524 to Moore et al. issued Jan. 7, 1997, U.S. Pat. No. 6,177,157 to Cota issued Jan. 23, 2001, and U.S. Pat. No. 6,231,944 to Holt issued May 15, 2001. These shields are useful to prevent heat transmitted from an engine""s high temperature components, such as the exhaust manifold, from reaching and damaging adjacent non-metal components. Examples of operating apparatus having non-metal components in need of protection include alternators, starter motors, turbo chargers, plastic storage containers for water and brake cylinder reservoirs wiring and tubing. These shields are also useful to reduce the transfer of noise and vibrations coming from the engine and various components of the exhaust system, including the manifold.
It is desirable that a heat shield for exhaust systems of internal combustion engines to meet the following criteria:
(a) to provide thermal shielding;
(b) to abate noise;
(c) to abate vibrations;
(d) strength to resist damage;
(e) to protect the engine/manifold from mechanical damage;
(f) recyclable; and
(g) easy and inexpensive to manufacture.
Known heat shields for exhaust systems of internal combustion engines include those formed of a single metal layer. Among the disadvantages of such shields are that they do not efficiently reduce noise, they have a tendency to vibrate, and that they are the least effective of all heat shield types in reducing conductive heat transfer. Known heat shields for exhaust systems of internal combustion engines include those formed of two metal layers of either equal or unequal thickness. Such shields tend to be superior in terms of ability to abate transfer of heat, noise and vibrations over shields formed of a single metal layer. However, the present inventor has appreciated that the ability of these shields to abate transfer of heat, noise and vibrations can be further improved.
Known heat shields for exhaust systems of internal combustion engines include those formed of two metal layers of either equal or unequal thickness, and a layer of insulating material (e.g. fiberglass, ceramic, aramid or air) sandwiched between the two metal layers. Such shields are, for example, described in U.S. Pat. Nos. 5,590,524 and 6,231,944. The present inventor has appreciated that such shields suffer from the disadvantages of not being recyclable, and of being relatively costly and inconvenient to manufacture because of the process steps required to include the layer of insulting material. Further, the present inventor has appreciated that the layer of insulating material is susceptible to damage, which is caused by periodic heat shock and vibration loads of the environment and by the moisture it can absorb, thus resulting in the disintegration of the fibers and reducing the serviceable life of such shields.
U.S. Pat. No. 5,590,524 describes a shield comprising two metal layers which have substantially different thicknesses and a layer of insulating material between the two metal layers. This patent is a good illustration of the approach that persons skilled in the art have taken in attempting to improve the thermal, acoustical and vibrational abatement properties of such shields. Persons skilled in the art expect that by providing layers which are different as in having substantially different thicknesses, these two layers would have mismatched resonant frequencies resulting in more efficient damping and absorption of acoustical and vibrational energy. Persons skilled in the art also expect that providing a third layer of insulating material would improve the damping properties of the shield by increasing the friction resisting the relative movement between the two metal sheets. Further, persons skilled in the art also expect that a third layer of insulating material would provide more shielding to thermal transmission by increasing the number of interface surface barriers within the shield. The present inventor has appreciated that surprisingly the use of different layers is not the best approach for producing shields with superior thermal, acoustical and vibrational abatement properties.
To at least partially overcome the disadvantages of previous heat shields, especially for applications where radiant heat management, damage protection, vibration control, noise emittance, recyclability, and geometrical restrictions are given higher priority than conductive heat management, the present invention provides a heat shield with improved acoustical and/or vibrational abatement properties. The present invention also provides a shield which has strength to resist damage, is recyclable, and is relatively easy and inexpensive to manufacture.
An object of the present invention is to provide a shield with improved thermal abatement properties compared to the previous double-layer metallic heat shields of identical overall thickness and comparable metallic materials.
A further object of the present invention is to provide a shield with improved acoustical abatement properties compared to the previous double-layer metallic heat shields of identical overall thickness and comparable metallic materials.
A further object of the present invention is to provide a shield with improved vibrational abatement properties.
A further object of the present invention is to provide a shield which has strength to resist damage better than any previous heat shield, including the ones with a layer of insulating material.
A further object of the present invention is to provide a shield which is recyclable.
A further object of the present invention is to provide a shield which has a longer serviceable life due to better vibration management.
A further object of the present invention is to provide a shield which has improved corrosion resistance without changing its base material and/or its coating.
A further object of the present invention is to provide a shield which is relatively easy and inexpensive to manufacture.
Accordingly, in one aspect, the present invention provides a heat shield for an exhaust system of an internal combustion engine, comprising three metal layers shaped to conform generally to the shape of a high temperature portion of said exhaust system; said metal layers having substantially the same shape and extending in face-to-face adjacency with one layer positioned between the other two layers; said three metal layers being substantially identical.
Preferably, said three metal layers are substantially identical in being of substantially the same thickness and composition.
Preferably, one of said three metal layers may differ in thickness from the other two metal layers by not greater than 20%, more preferably not greater than 15%, or 10%, or 5%.
Preferably, two of said three metal layers have an identical thickness, and more preferably, all said three metal layers have an identical thickness.
Preferably, each of said metal layers has a thickness of between about 0.25 mm and about 0.5 mm, more preferably between about 0.30 mm and about 0.45 mm, or between about 0.35 mm and about 0.40 mm.
Preferably, each of said metal layers has a thickness of about 0.34 mm.
Preferably, each of said three metal layers comprise the same base metals; or two of said three metal layers comprise the same base metals and the remaining layer comprises material that is an alloy of the material of the other two layers; or each of said three metal layers comprises material that is an alloy of the material in at least one of the other two layers.
Preferably, each of said metal layers comprises materials selected from the group consisting of aluminized steel, aluminum coated steel, aluminum cladded steel, and galvanized steel.
Preferably, said heat shield is manufactured by a process under which said metal layers are compressed together under pressure.
Preferably, each of said metal layers has a non-planar shape.
Preferably, each of said metal layers is deep drawn to a ratio of depth to thickness of from about 5:1 to about 100:1, more preferably from about 10:1 to about 75:1, or from about 15:1 to about 50:1.
Preferably, hems are provided along at least some edges of said heat shield to maintain said metal layers nested together.
Preferably, the exterior surface of said shield is coated with a coating effective to provide corrosion-resistant protection to said shield.
Preferably, the exterior surface of said shield is coated with a coating effective to provide heat reflection.
Preferably, said coating is high temperature resistant.
Preferably, said high temperature portion of said exhaust system is an exhaust manifold.
Preferably, said high temperature portion of said exhaust system is selected from the group consisting of a catalytic converter, a muffler, and an exhaust pipe.
Preferably, the shield is spaced away from the exhaust system by an air gap, with preferably, a significant portion of said air gap being between about 1 mm and about 30 mm, more preferably between about 3 mm and about 15 mm wide.